Process of manufacturing hot vulcanized froth from india-rubber, gutta-percha, and balata.



resent, so much as is known at present, a

canizing temperature.

, UNITED STATES PATENT OFFICE- FRITZ .PFLEUMER, 0F DRESDEN, GERMANY.

rnocnss or MANUFAGTUBING Ho'rvuLcANIzEn rno'rn rnom INDIA-RUBBER,

GUTTA-PERQHA, AND BALA'IA.

No Drawing.

Specification of Letters Patent. Patented Sept. 17, 1912.

Application filed July 26, 1911. Serial No. 640,648.

Froth from India Rubber, Gutta Percha,

and Balata, of which the following is a specification.-

Processes of manufacturing elastic froth from, glycerin-gelatin, india rubber or similar substances, used for elastic tire fillings or other purposes, are described in the following patents: Germany Nos. 60,230 and 92,208, Great Britain No. 22,640/07, United States Nos. 7 53,206 and 753,300, Germany Nos. 174,001 and 185,306, Great Britain Nos. 3314/06 and 13,390/09, France NOS. 329,117 and 402,996.

In the first-mentioned two German patents it is suggested to raise the frothor sponge-structures by mixing into the india rubber chemicals yielding gases at the vul- In the next-mentioned patent it is proposed to add to the glycerin-gelatin chemicals which on coming in contact with the moist matter generate carbonic acid, and to use the thus produced gas as froth-raising medium. In the processes of the other patents mentioned above an optional gas is brought into the mass by mechanical treatment as beating, stirring, kneading, shaking or centrifuging said mass under an atmosphere of the respective gas, or by injecting the gas into the mass.

Processes of hot vulcanizing solid rubber articles under an atmosphere of a hot inert gas as nitrogen or carbon dioxid are described in the British Patent No. 7159/01 and United States Patent No. 661,177. In these processes it is intended to revent air eventually included by the rub er or the vapors of the sulfur generated at the vulcanizing temperature from raising pores or bubbles by carrying out the vulcanizatlon under pressure of said gases up to about 100 pounds per square inch or about 7 atmospheres, the gas-pressure thereby acting as mechanical counter-pressure agalnst the raising of bubbles.

I have based my invention upon the observation that india rubber as well as guttapercha and balata are by no means homo-' geneous or impenetrable substances, but repreticular structure justvisible under the best mlcroscopes, into which structure gas can penetrate or pass through it under certain condit ons. (Literature: 0. O. Weber, The Chem stry of India Rubber, page 19, Wroblewskis conclusions 3, 5 and 11; page 78, line6 and 11 to 18.)

A iece of raw rubber submitted in an autoc ave to a high pressure (from 80 to 300 atmospheres) of an optional gas, air, nitrogen etc., on being relieved of the gaspressure, shows a considerable increase of .1ts bulk and a crackling, which originates from small bubbles bursting on the surface of the piece. On ceasing of the crackling the rubber piece has regained almost its original volume. The thus treated piece on superficial inspection shows a great number of pores, obviously channels worked by the gas on its way into, and out of, the rubber piece. The effect increases, if the rubber previously to its being subjected to high gas pressure is soaked in about one quarter of its weight of any rubber solvent, for instance benzene. If, however, the rubber piece is kneaded together with from 2 to 10% of its weight of precipitated sulfur and the piece subjected under the above mentioned gas-pressures to the vulcanizing temperature, 135 to 145 C., for about two hours, "the piece on being relieved of the ext 'nal gas-pressure does no more allow its contents of gas to'escape, and

consequently expands to ahighlyvoluminous and regular froth in'the cells of which the gas is permanently imprisoned. In this case the action .of the gas upon the india rubber is a direct-1y opposite one to the ac-. tion mentioned in the last cited two Tspe'cifications. Such highly compressed gas acts no more as counter-pressure against any raising of bubbles, but penetrates the india rubber, filling up all the pores of the microscopic structure.

Experience teaches that india rubber in froth. In the stretched state the films are.110

, gas-tight in spite of'the structure of the material. It must be considered that the natural structure of the material has the appearance of a sponge. the channels and walls of which are of smaller dimensions than the artificial froth structure forced upon the material by the described treatment.

It is not a condition of the process that the raw rubber should contain any solvent,

an addition by weight of one quarter of benzene or benzol, however, allows of con fifth to one part of precipitated sulfur; op-

' tionally according to the desired effect the rubber previously to the kneading may be soaked in about two parts of benzene or beuzol. In conjunction with the sulfur ans timony pentasulfid, so-called golden sul fid may be employed advantageously. The

thus made dough is now formed into articles, the form of which is geometrically similar to the form the respective article is intended to have after transformation into froth. The proportions in sizes of the pieces formed of the rubber dough on the one side and the finished froth piece on the other naturally depend on the quantity of gas the finished froth piece is intended to contain.

When vulcanized under a pressure of about 100 atmospheres the finished froth in the expanded and dry state contains about 9 parts by volume of gas in every one part of rubher, i. e., about 13 parts by volume of the rubber dough must be chosen for making a froth piece of 100 parts by volume. From this the linear proportions may be derived. If the solvent is left out, in order to attain the above mentioned proportions of the volume, about 300 atmospheres gas-pressure, gaged at the vulcanizing temperature, are required. The shaping is carried out by either pressing the dough into molds, or for simple sectional pieces by squeezing the dough from a tubing machine with a mouthpiece of the required section into endless bars or rods. 7

The reception of gas may be considerably increased by mixing into the mass porous materials in a pulverous state, for instance Kieselguhr, ground cork, bone-black factice etc. In this case beside the mass each grain into its pores is receiving gas which on expansion'leaves the ain forming one cell in the interior of whicli the grain remains. The pieces are now vulcanized in an autoclave under high pressure of a gas. Nitrogen,

carbon monoxid, eventually air are suited to the purpose, while hydrogen and carbon dioxid, so-called carbonic acid, are precluded from the technical application on account of their diffusing properties as well as oxygen on account of its oxidizing action on rubber. It is of course impossible to let steam into an autoclave filled with gas under so high a pressure. The autoclave has therefore to be heated with steam from without. Also india rubber which is already vulcanized and contains no more than 10% of free sulfur, may be thus transformed into froth; it should, however, contain only small quantities of other admixtures in order to attain a froth sufliciently gas-tight for the purpose in view. A small quantity of free sulfur is always present in soft vulcanized rubber, and generally suflices to attain an additional vulcanization, which renders the froth raised stable. Thus old motor-car tubes or waste of vulcanized sheets may directly be transformed into froth sheets, and these worked up into inlayingsfor life-saving dresses, heels, billiard cushions, sound proof mats for typewriters and musical instrufnents, etc.

From the fact that vulcanized material can be transformed into froth an alteration of the described process of making froth from raw material'may be derived in that direction that the raw material be vulcanized first without gas-pressure, and be placed under gas-pressure afterward. In this case, however, the material should be kept rather hot in order to carryout vulcanization and froth raising in one uninterrupted operation. This optional way has the disadvantage of thematerial being longer heated than in the process already described.

For many applications, as, for instance, cycle and motor-car tires the froth must contain its gas filling under a certain pressure. To subsequently compress rubber-froth that has been expanded to the atmospheric pressure in order to make froth filled with gas under pressure would be a failure, as it is a matter of experience that the films on recontraction lose their gastightness. -Therefore the froth already after vulcanization should not be expanded down to a lower pressure than is required for its application. This-pressure amounts to from 2 to 3 atmospheres (28 to 42 pounds per square inch) for cycle tires and 'from t} to 8 atmospheres (63 to112 pounds per square inch) for motor-car tires. One of the following methods may be applied for making such froth containing gas under pressure:

1. Raw material of high tensile strength is treated in the described manner, no solvent being applied. When the vulcanization is finished the articles are left under pressure for several hours so that they may cool out and regain their original tensile strength previously to being expanded into froth. Part of the gas in the autoclave may be let out directly after vulcanization with the purpose of starting formation of the froth structure. The gas coolin out after vulcanization its pressure furt er decreases.

2. Into the raw material, when being mixed with the ingredients, fibrous substances as, for instance, fibers of raw cotton, raw jute or raw hemp are kneaded. These fibers should be no longer than about 3/16th of an inch (5 mm) otherwise they would conglobate into lumps. By the quantity of fibers admixed the pressure, at which further expansion ceases, may be fixed.

By means of these methods interchangeable tire cushions are made, which upon account of their being gas elastic and indestructible bv punctures represent a suit-able substitute for air-tubes. They do not expand so far on being dismounted from a worn-out cover as to impede their being mounted under a new one.

Analogous to the described, the process is carried out with guttapercha and balata. These are kneaded with from 5 to 10% of precipitated sulfur, optionally with an addition of antimon pentasulfid. In the trade this chemical is to be had with an admixture of up to of free sulfur, and 10% of it, containing 5% of the raw materials weight of free sulfur, give a grade of vulcanization best suited to the purpose. Also soft vulcanized guttapercha and balata may be transformed into froth in the described manner. With this process one can also manufacture froth of hard rubber, hard guttapercha and hard balata. To this end a 'dough containing from 30 to 50% of sulfur is used, the articles vulcanized under gaspressure, and expanded when still. hot. The

vulcanization is continued on the expanded froth until the hard state is reached. The expansion must be carried out on the hot froth as otherwise it would contract on being further vulcanized. Hard vulcanized froth is used in cases, where no elastic Having thus fully described my invention,

what I claim as new and desire to secure by Letters Patent of the United States is:

1. A process for manufacturing hot vulcanized froth from .india rubber, guttapercha and balata, consisting in hot vulcan- 1zing raw or partly vulcanized material, under such ahigh pressure of a gas that the gas penetrates the structure of the material, and on partly or wholly releasing the external gas-pressure raises the mater1al into froth.

2. A process for manufacturing hot vulcanized froth from india rubber, guttapercha and balata, consisting in keeping the thus treated material under high gas-pressure, so that the gas penetrates the structure of the material, until it is cooled, and afterward releasing it of the gas pressure in order .to produce .froth containing more than atmospheric pressure.

In testimony whereof I aflix my signature in presence of two witnesses.

' FRITZ PFLEUMER. Witnesses:

PAUL AREAS, FRANZ NETCHE. 

